Laminated corrugated coaxial cable structure and method for making

ABSTRACT

The outer conductor of a coaxial cable is made by separately corrugating a steel tape and a copper-steel strip in two mated and contiguous mills. The formed members are then edge-registered with the steel tape overlapping the strip; and tubed together to butt the steel tape edges. These thereafter are soldered closed. Advantageously the strip edges are 180* removed from the solder joint.

United States Patent (72] Inventor David J. Meske11,.lr. 2,733,288 1/1956 Webster 174/106 X Bllicott City, Md- 3,183,300 5/1965 Jachimowicz et a1. 174/106 [21] Appl. No. 844,347 3,360,409 12/1967 Jachimowicz et a1 174/106 (UX) [22] Filed July 24, 1969 3,373,475 3/1968 Petersen 174/106 (UX) [451 Patente III: 22. 1971 3,405,228 10/1968 Polizzano 174/106 1 1 ig BellTelephone Labwmvriw Incorporated 3,430,330 3/1969 Garner 174/102 x Murray Hill, Berkeley Heights, NJ. FOREIGN PATENTS m 573,261 11/1944 Great Britain 174/106 [54] LAMlNATED CORRUGATED COAXIAL CABLE 848,495 10/1939 France 156/54 STRUCTURE AND METHOD FOR MAKING primary Examine, Lewis Myers 5 cum, 6 Drum Assistant Examiner-A. T. Grimley 52 vs. C! 174/106, y Guemher and Edwin Cave 156/54, 174/28, 174/36 [51] Int. Cl H0111 7/20,

1 H18 ABSTRACT: The outer conductor of a coaxial cable is made 0f Separately ti a t l t d a t l t i 170, 171; 174/ 106, 36, 105, 7 0 in two mated and contiguous mills. The formed members are then edge-registered with the steel tape overlapping the strip; [56] References and tubed together to butt the steel tape edges. These UNTED STATES PATENTS thereafter are soldered closed. Advantageously the strip edges 2,589,700 3/ 1952 Johnstone 174/ 106 are 180 removed from the solder joint.

PATENTED JUH22 I97! INVENTOR D. J. MES/(ELL AT TORNEV LAMINATED CORRUGATED COAXIAL CABLE STRUCTURE AND METHOD FOR MAKING FIELD OF THE INVENTION This invention relates to coaxial communications cable, and particularly to an improved outer conductor structure and method for fabricating same.

BACKGROUND OF THE INVENTION The currently manufactured coaxial cable typically has an outer conductor of thin copper laminated adhesively to tinplated steel. In manufacture, this strip is corrugated to provide bendability and crush resistance, and thereafter is formed as a tube around an inner conductor. The tube seam is soldered in a manner described in the patent application of M. C. Biskeborn et al., Ser. No. 812,517, filed Feb. 20, 1969. Soldering fixes the electrical diameter of the outer conductor, electrically shields the transmission path within,and hermetically seals the cable.

In the forming operation described, in order to assure a strong seam, the edges are overlapped slightly at the seam, and the solder is applied adjacent to the overlap where it flows by capillary action into the narrow overlap region.

Although generally satisfactory as to cost, manufacturability and performance, the outer coaxial cable-conductor forming procedure has disadvantages, as does the resulting structure. For example, in order for the corrugations to match at the overlap joint, as they must, a transverse nonuniformity in corrugation profile must be imparted. This operation produces a different takeup at the corrugation edges and tends to bow the strip. Because of this bow, or camber, the later forming operations are made more difficult, and in addition undesired material stresses are generated at the profile transition. Also, the special corrugators required are quite expensive.

Moreover, to ensure that the exterior edge will lie flat at the overlap, and not tend to lift off, it is necessary to overform'that edge. This represents an added complication in forming the strip with attendant increases in forming roll costs and risk of damage.

Additionally, due to the edge overlap, wetting action in the soldering stage is severely limited. Contaminating particles, if present, readily thwart the wetting and cause hermetic sealdestroying pinholes or skips.

A further and more general problem in the above-descri bed coaxial cable outer conductor is that the seam inherently projects and can interact mechanically with the stranding process and other such seams. One result of such interaction is occasional perturbations which can cause deviation in transmission characteristics within a cable. This can also act as a stress raiser in the case where single units are produced with polyethylene jackets.

Accordingly, a major object of the invention is to simplify the construction of a laminated, corrugated outer conductor for a coaxial communications cable.

A further object of the invention is to simplify production steps as to the outer conductor of such cable.

A further object of the inventionis to improve the mechanical and hermetic properties of the joint in a formed-laminated.- corrugated-type outer conductor.

A specific object of the invention is to eliminate the projecting seam of the joint in a laminated-corrugated-type outer conductor.

SUMMARY OF THE INVENTION copper-steel strip and the interior surface of the steel tape are of the same geometry. After corrugating, the two members undergo forming by stages toward a circular configuration. At some such stage, such as when the two members are formed to the semicircular point, their mated corrugations are caused to self-register. Thereafter, further-forming stages tube. the members in unison and ultimately the steel-tape edges substantially butt. These edges thereafter'are soldered closed.

A key aspect of the invention is that in the resulting structure, the edges of the interior strip are angularly removed from the solderjoint; and in the outer strip edge-joint region, a firm and uninterrupted interface for solder wetting exists.

Further important advantages are exhibited by the inventive structure. The corrugations, for example, across both tapes are uniform which eliminates both expensive corrugators and the tendency of the product to bow or have permanent.

locked-in stresses. Moreover, since the joint is not overlapped, the structure is more regular, and the load on the solder joint is both lower and more even.

As there is no transverse nonuniformity in the corrugations, not only is this stage eliminated in the present invention} but the further treatments of such edge in later forming stages also are eliminated.

The solder joint of the present invention is particularly strong. Solder is simply puddled into the edge region, and flows in both directions for substantial distances beyond the joint itself. If, as is advantageous, the interior member edge is angularly removed from the exterior edges by the wetting region can embrace substantially the entire interface between the outer and inner members. A hermetic seal thus is virtually guaranteed.

-Most importantly, from a performance standpoint, elimination of the projecting seam avoids the stranding interaction and the possible'transmission deviations that arise therefrom.

The invention and its further objects, features and advantages will be readily apprehended in full from a reading of the detailed description to follow of an illustrative embodi ment thereof.

DESCRIPTION OF THE DRAWING FIG. I is a schematic side perspective view of a coaxial cable whose outer conductor is constructed in accordance with'the present invention;

FIG. la is a cross-sectional view of the completed outer conductor;

FIG. 2 is a schematic diagram of a process illustrative of the method of fabricating such an outer conductor; and

FIGS. 3, 4, and 5 are sectional views across the outer conductor strips, taken at specific stages of the process.

DETAILED DESCRIPTION OF AN ILLUSTRATIVE EMBODIMENT The inventive structure of the coaxial cable outer conductor will first be described; and thereafter a process suitable for its manufacture will be disclosed.

STRUCTURE As seen in FIG. 1, a coaxial cable 10, constructed in accordance .with the inventive teachings, includesthe usual inner conductor 1] supported, for example at intervals by discs 12 within an outer conductor 13. Outer conductor 13 consists of an interior member 14, which, for example, can be a 4-mil thick copper strip bonded metallurgically or adhesively laminated to a 3-mil thick tin-plated steel strip. Outer conductor I3 further consists of exterior member 15 which, for example, can be a 6- or: 7-mil thick tin-plated steel strip.

The two members 14 and .15 are given corrugations of a geometry that, when the members are later tubularly formed, enables them to precisely register along their entire interface 16. The edges 14a, 14b of interior member 14 are formed so as to abut Abutting of edges 14a, 14b can be used to help size the coaxial.

Exterior member is formed so that its edges 15a, 15b are spaced a distance from one another in the range 30 to 60 mils. In this space, a head of solder 17 is puddled in. As shown in FIG. la, the solder l7 draws by capillary action away from the edges 15a, 15b, along the interface 16, typically a distance of l25 to 250 mils which distance is controlled by proper heat application and the amount of solder used. The bead of solder 17 tends to conform to the corrugated contour of exterior member 15 so that a relatively smooth continuous surface with no projecting seam is achieved.

METHOD OF MANUFACTURE FIG. 2 depicts in schematic form a fabricating line for the construction of the above-described coaxial cable. The line commences with a source such as reel 20 of a first metal strip 21 from which interior member 14 is to be made; and a reel such as 22 for a second metal strip 23 from which exterior member 15 is to be made. Also, a source 19 of inner conductor 11 outfitted with spacing discs 12 is provided.

The strip 21 for interior member 14 advantageously is a composite of a 4-mil thick copper strip bonded metallurgically or laminated to a 3-mil thick tin-plated steel strip. Strip 23 for exterior member 15 is advantageously tin-plated steel 6 or 7 mils thick. The copper side of strip 21 is oriented so that in later-forming stages that side will face the cable interior to supply the high conductivity outer conductive path.

Pursuant to one aspect of the invention, the overall thicknesses of each of the strips 21, 23, are selected to achieve equal pullout. That is, they exhibit equal elongation for a given applied tensile force when in corrugated form. Equal pullout is desirable to facilitate forming in the later stages and to insure proper corrugation matching' Numerous alternate material combinations are suitable in selecting the strips 21, 23. For example, an all-copper metal strip 21 of 10 mils thickness can be teamed with a tin-plated steel strip 23' of 6 mils thickness, these dimensions being chosen for their efiectuation of the pullout equivalency, assuming corrugation profile differences have negligible effect. The exact balance in a given case takes account of corrugation shape, roll ironing, and desired transmission characteristics (i.e., Cu thickness).

The flat metal strips 21, 23 are respectively fed to corrugators 24, 25, which impart to the strips uniform transverse corrugations. In accordance with the invention, the corrugators are machined and matched in profile to produce substantially geometrically equal surfaces in respect to the inner side of strip 23 and the outer'side of strip 21. The mentioned sides, as can be seen in FIGS. 1 and la, are ultimately tightly interfaced in the completed cable, after further forming stages. Additionally, corru'gators 24, 25 are geared together by suitable means 37 so as to produce and maintain the now-corrugated strips 21, 23 in phase to promote their self-registration at the conjoining point.

Following corrugation, the strips 21, 23 undergo one or more stages of forming in which transverse curvature is produced therein by conventional forming mills such as 26, 27. The degree of transverse curvature imparted to the strips 21, 23 is determined by considerations relating to the setup at the conjoining mill 28, 29 where the two strips first contact.

Thus, as seen in FIG. 3, one possible pair of curvatures for the strips 21, 23 are semicircles in cross section. Alternatively, however, the interior strip 21 can be formed entirely into a circular configuration before the mating with strip 23. lnnumerable intermediary degrees of curvature are, of course, envisionable. 1

Between the forming mill 26, 27 and the conjoining mill 28, 29 it is desirable to allow slack in the strips 21, 23, to facilitate their self-registry at or slightly prior to arrival at the conjoining mill. Also, for certain transverse curvatures of interior strip 21, which are not significantly more than 180", it is desirable to champfer the strips edges 14a, 14b inwardly as shown in FIG. 4.

In the instant example, at the conjoining mill 28, 29, strip 21 is introduced into the interior of strip 23, the two strips being in self-registration by virtue of their mating corrugations. Conjoining mill 28, 29 forms the now-corrugated and partially circular strips 22, 23 into the FIG. 4 configuration; or, alternatively, effects a deeper penetration of the one strip into the other. Subsequent forming in the mills 31, 32 completes the forming of the outer conductor 13, which by now has the configuration depicted in FIG. 5.

Thereafter, the outer conductor is heated as with inductive heating elements 33 preparatory to application of solder through feed 34 into the seam formed by edges 15a, 15b shown in FIGS. 1 and la. The solder seam follows the contour of the exterior surface of member 15 to create a smooth protrusion-free seam. Much enhanced mechanical strength is afforded by the capillary movement .of solder in the interface area 16. The same solder structure also provides a fully reliable hermetic seal in which particulate matter, if it be present, is not fatal. The soldered coaxial cable is transported as by belts 35 to a reel 36 where the finished cable is collected in conventional fashion.

The edges 14a, 14b of interior member 14 are, in the instant embodiment, diametrically opposite the solder seam. Angular separations of less than I are, of course, also within the teaching.

The spirit of the invention is embraced in the scope of the claims to follow.

lclaim:

1. A coaxial communications cable comprising an inner and an outer conductor, in which the outer conductor is characterized by an interior and a contiguous exterior member each formed from strip material, each said strip being transversely corrugated with corrugation profiles selected such that the contiguous surfaces of said members are of the same geometry, the opposing edges of said exterior member being in nonoverlapping juxtaposition forming an open joint therebetween, the opposing edges of said interior member being substantially angularly separated from said exterior member edges, and means for mechanically sealing said joint.

2. A cable pursuant to claim 1, further characterized in that thesaid sealing means comprises a solder seam applied in said joint to conform to the exterior member outer surface configuration, said solder seam extending along at least a portion of the interface zone between said members on either side of said joint. f

3. A cable pursuant to claim 1 further characterized in that said angular separation is substantially 4. A cable pursuant to claim 2 further characterized in that said angular separation is substantially 180 and in that said interface zone is tin-plated steel.

5. A cable pursuant to claim 2, wherein the opposing edges of said interior edge abut. 

1. A coaxial communications cable comprising an inner and an outer conductor, in which the outer conductor is characterized by an interior and a contiguous exterior member each formed from strip material, each said strip being transversely corrugated with corrugation profiles selected such that the contiguous surfaces of said members are of the same geometry, the opposing edges of said exterior member being in nonoverlapping juxtaposition forming an open joint therebetween, the opposing edges of said interior member being substantially angularly separated from said exterior member edges, and means for mechanically sealing said joint.
 2. A cable pursuant to claim 1, further characterized in that the said sealing means comprises a solder seam applied in said joint to conform to the exterior member outer surface configuration, said solder seam extending along at least a portion of the interface zone between said members on either side of said joint.
 3. A cable pursuant to claim 1 further characterized in that said angular separation is substantially 180*.
 4. A cable pursuant to claim 2 further characterized in that said angular separation is substantially 180* and in that said interface zone is tin-plated steel.
 5. A cable pursuant to claim 2, wherein the opposing edges of said interior edge abut. 